-- lib-core.puppet v0.1.0
-- Skeletal animation: skeleton + bones + tracks + rest + keyframe
-- + procedural + look-at constraint. No footplant in v0.1.

local M = {}

-- ====================================================================
-- Module state (lib-singleton)
-- ====================================================================
local all_puppets   = {}  -- {[handle] = puppet_instance}
local next_handle   = 1

-- ====================================================================
-- Utility helpers
-- ====================================================================
local function deep_copy(t)
    if type(t) ~= "table" then return t end
    local copy = {}
    for k, v in pairs(t) do copy[k] = deep_copy(v) end
    return copy
end

local function clamp_angle_rad(a)
    -- Normalize to [-pi, pi]
    local pi = math.pi
    while a > pi do a = a - 2 * pi end
    while a < -pi do a = a + 2 * pi end
    return a
end

-- Subsequent tasks add: sample_animation,
-- spawn, despawn, update, render, set_look_target, clear_look_target,
-- bone_angle, set_procedural, clear_procedural, write_bone, play, stop,
-- stop_all, is_playing, position, facing, move_to, register_animation,
-- load_rig, load_animation.

-- ====================================================================
-- Rig validation + build
-- ====================================================================
function M.build_rig(rig_table)
    if type(rig_table) ~= "table" then
        error("puppet.build_rig: rig_table must be a table")
    end
    if type(rig_table.bones) ~= "table" or #rig_table.bones == 0 then
        error("puppet.build_rig: rig.bones must be a non-empty array")
    end
    if type(rig_table.tracks) ~= "table" then
        error("puppet.build_rig: rig.tracks must be an array")
    end

    -- Build bones_by_id with shallow copies of rest pose.
    local bones_by_id = {}
    for _, b in ipairs(rig_table.bones) do
        if type(b.id) ~= "string" then
            error("puppet.build_rig: bone.id must be string")
        end
        if bones_by_id[b.id] ~= nil then
            error("puppet.build_rig: duplicate bone id: " .. b.id)
        end
        bones_by_id[b.id] = {
            id = b.id,
            parent = nil,  -- resolved below
            rest = {
                x = b.rest.x, y = b.rest.y,
                -- JSON angles in degrees; convert to radians once.
                angle = math.rad(b.rest.angle or 0),
            },
            look_at = (b.look_at == true),
            color = b.color or { 200, 200, 200 },
        }
    end

    -- Resolve parents (object references).
    for _, b_src in ipairs(rig_table.bones) do
        local b = bones_by_id[b_src.id]
        if b_src.parent ~= nil then
            local parent_obj = bones_by_id[b_src.parent]
            if parent_obj == nil then
                error("puppet.build_rig: parent '" .. tostring(b_src.parent)
                      .. "' of bone '" .. b.id .. "' not found")
            end
            b.parent = parent_obj
        end
    end

    -- Build tracks + validate each bone is in EXACTLY ONE track.
    local bone_to_track = {}
    local tracks_by_id = {}
    for _, t in ipairs(rig_table.tracks) do
        if type(t.id) ~= "string" then
            error("puppet.build_rig: track.id must be string")
        end
        if tracks_by_id[t.id] ~= nil then
            error("puppet.build_rig: duplicate track id: " .. t.id)
        end
        local bones_in_track = {}
        for _, bid in ipairs(t.bones) do
            if bones_by_id[bid] == nil then
                error("puppet.build_rig: track '" .. t.id
                      .. "' references unknown bone '" .. bid .. "'")
            end
            if bone_to_track[bid] ~= nil then
                error("puppet.build_rig: bone '" .. bid
                      .. "' assigned to multiple tracks ('"
                      .. bone_to_track[bid] .. "' and '" .. t.id .. "')")
            end
            bone_to_track[bid] = t.id
            bones_in_track[#bones_in_track + 1] = bid
        end
        tracks_by_id[t.id] = { id = t.id, bones = bones_in_track }
    end

    return {
        id = rig_table.id or "anonymous",
        bones = rig_table.bones,           -- keep original-order array
        bones_by_id = bones_by_id,
        tracks_by_id = tracks_by_id,
        bone_to_track = bone_to_track,
    }
end

-- ====================================================================
-- Animation validation + build
-- ====================================================================
function M.build_animation(anim_table, rig)
    if type(anim_table) ~= "table" then
        error("puppet.build_animation: anim_table must be a table")
    end
    if type(anim_table.track) ~= "string" then
        error("puppet.build_animation: animation.track must be string")
    end
    if rig.tracks_by_id[anim_table.track] == nil then
        error("puppet.build_animation: animation.track '"
              .. anim_table.track .. "' not found in rig")
    end
    if type(anim_table.duration) ~= "number" or anim_table.duration <= 0 then
        error("puppet.build_animation: animation.duration must be positive number")
    end
    if type(anim_table.keyframes) ~= "table" or #anim_table.keyframes == 0 then
        error("puppet.build_animation: animation.keyframes must be non-empty array")
    end

    -- Validate each keyframe: t in [0, duration], bones referenced are in this animation's track.
    local track_bones = {}
    for _, bid in ipairs(rig.tracks_by_id[anim_table.track].bones) do
        track_bones[bid] = true
    end

    local keyframes = {}
    for i, kf in ipairs(anim_table.keyframes) do
        if type(kf.t) ~= "number" or kf.t < 0 or kf.t > anim_table.duration + 1e-9 then
            error("puppet.build_animation: keyframe[" .. i .. "].t out of [0, duration]")
        end
        local cooked = { t = kf.t, bones = {} }
        for k, v in pairs(kf) do
            if k ~= "t" then
                if rig.bones_by_id[k] == nil then
                    error("puppet.build_animation: keyframe references unknown bone '" .. k .. "'")
                end
                if not track_bones[k] then
                    error("puppet.build_animation: keyframe writes bone '" .. k
                          .. "' which is not in animation's track '" .. anim_table.track .. "'")
                end
                cooked.bones[k] = {
                    angle = v.angle or 0,  -- keep in degrees; interpolation stays in degrees
                }
            end
        end
        keyframes[i] = cooked
    end

    return {
        id = anim_table.id or "anonymous",
        track = anim_table.track,
        duration = anim_table.duration,
        loop = (anim_table.loop == true),
        keyframes = keyframes,
    }
end

-- ====================================================================
-- Animation sampling
-- ====================================================================
function M.sample_animation(anim, t)
    -- Wrap t for loops.
    if anim.loop and t > anim.duration then
        t = t % anim.duration
    end
    if t < 0 then t = 0 end
    if t > anim.duration then t = anim.duration end

    local kfs = anim.keyframes
    -- Find segment [kf_i, kf_{i+1}] containing t.
    local prev_kf, next_kf = kfs[1], kfs[1]
    for i = 1, #kfs - 1 do
        if t >= kfs[i].t and t <= kfs[i + 1].t then
            prev_kf = kfs[i]
            next_kf = kfs[i + 1]
            break
        end
    end

    -- If t equals last keyframe's t (or beyond and not looping), snap to last.
    if t >= kfs[#kfs].t then
        prev_kf = kfs[#kfs]
        next_kf = kfs[#kfs]
    end

    -- Linear interpolation per bone present in either keyframe.
    local frame = {}
    local span = next_kf.t - prev_kf.t
    local alpha = (span > 0) and ((t - prev_kf.t) / span) or 0

    local all_bones = {}
    for bid, _ in pairs(prev_kf.bones) do all_bones[bid] = true end
    for bid, _ in pairs(next_kf.bones) do all_bones[bid] = true end

    for bid, _ in pairs(all_bones) do
        local prev_v = prev_kf.bones[bid]
        local next_v = next_kf.bones[bid]
        if prev_v and next_v then
            frame[bid] = {
                -- keyframe angles are stored in degrees; interpolate in degrees.
                angle = prev_v.angle * (1 - alpha) + next_v.angle * alpha,
            }
        elseif prev_v then
            frame[bid] = { angle = prev_v.angle }
        elseif next_v then
            frame[bid] = { angle = next_v.angle }
        end
    end

    return frame
end

-- ====================================================================
-- Puppet instance lifecycle
-- ====================================================================
function M.spawn(rig, pos)
    if type(rig) ~= "table" or rig.bones_by_id == nil then
        error("puppet.spawn: rig must be a built rig (use puppet.build_rig)")
    end
    pos = pos or { x = 0, y = 0 }
    local handle = next_handle
    next_handle = next_handle + 1

    -- Per-bone live state (current angle, current world-pos cache).
    local bone_state = {}
    for bid, b in pairs(rig.bones_by_id) do
        bone_state[bid] = { angle = b.rest.angle, world_x = 0, world_y = 0 }
    end

    all_puppets[handle] = {
        handle = handle,
        rig = rig,
        x = pos.x, y = pos.y,
        facing = 0,
        last_move_x = pos.x, last_move_y = pos.y,
        bone_state = bone_state,
        look_target = nil,
        animations = {},    -- {[anim_id] = built_anim}
        playing = {},       -- {[anim_id] = { t = 0, loop, speed }}
        procedural = {},    -- {[name] = callback_fn}
        write_target_bone = nil,  -- set during procedural callback to track track-conflicts
        write_target_track = nil,
    }
    return handle
end

function M.despawn(handle)
    all_puppets[handle] = nil
end

function M.position(handle)
    local p = all_puppets[handle]
    return { x = p.x, y = p.y }
end

function M.facing(handle)
    return all_puppets[handle].facing
end

function M.move_to(handle, x, y)
    local p = all_puppets[handle]
    local dx = x - p.x
    local dy = y - p.y
    if dx ~= 0 or dy ~= 0 then
        p.facing = math.atan(dy, dx)
        p.last_move_x = x
        p.last_move_y = y
    end
    p.x = x
    p.y = y
end

-- ====================================================================
-- Animation registration + playback control
-- ====================================================================
function M.register_animation(handle, anim)
    local p = all_puppets[handle]
    p.animations[anim.id] = anim
end

function M.play(handle, anim_id, opts)
    local p = all_puppets[handle]
    if p.animations[anim_id] == nil then
        error("puppet.play: animation '" .. tostring(anim_id) .. "' not registered")
    end
    opts = opts or {}
    p.playing[anim_id] = { t = 0, loop = (opts.loop == true), speed = (opts.speed or 1.0) }
end

function M.stop(handle, anim_id)
    all_puppets[handle].playing[anim_id] = nil
end

function M.stop_all(handle)
    all_puppets[handle].playing = {}
end

function M.is_playing(handle, anim_id)
    return all_puppets[handle].playing[anim_id] ~= nil
end

-- ====================================================================
-- Look-at + bone queries
-- ====================================================================
function M.set_look_target(handle, world_x, world_y)
    all_puppets[handle].look_target = { x = world_x, y = world_y }
end

function M.clear_look_target(handle)
    all_puppets[handle].look_target = nil
end

function M.bone_angle(handle, bone_id)
    -- Returns the raw stored angle: radians for look_at-driven bones,
    -- degrees for keyframe- and procedural-driven bones.
    return all_puppets[handle].bone_state[bone_id].angle
end

-- ====================================================================
-- Procedural layer
-- ====================================================================
function M.set_procedural(handle, name, callback)
    if type(callback) ~= "function" then
        error("puppet.set_procedural: callback must be function")
    end
    all_puppets[handle].procedural[name] = callback
end

function M.clear_procedural(handle, name)
    all_puppets[handle].procedural[name] = nil
end

function M.write_bone(handle, bone_id, values)
    local p = all_puppets[handle]
    -- Validate this bone's track is not currently keyframe-active.
    local track_id = p.rig.bone_to_track[bone_id]
    if track_id == nil then
        error("puppet.write_bone: bone '" .. bone_id .. "' not in rig")
    end
    -- A track is keyframe-active if any playing animation uses it.
    for anim_id, _ in pairs(p.playing) do
        local anim = p.animations[anim_id]
        if anim and anim.track == track_id then
            error("puppet.write_bone: bone '" .. bone_id
                  .. "' is on track '" .. track_id
                  .. "' currently active by keyframe '" .. anim_id .. "'")
        end
    end
    if values.angle ~= nil then
        -- Store the caller-supplied value directly; write_bone accepts degrees
        -- (same units as rest-pose angles and keyframe angles).
        p.bone_state[bone_id].angle = values.angle
    end
end

-- ====================================================================
-- Update pipeline (per-frame)
-- ====================================================================
function M.update(dt)
    for handle, p in pairs(all_puppets) do
        -- 1. Reset bones to rest pose.
        for bid, b in pairs(p.rig.bones_by_id) do
            p.bone_state[bid].angle = b.rest.angle
        end

        -- 2. Apply look-at constraint (writes to bones marked look_at: true).
        if p.look_target ~= nil then
            for bid, b in pairs(p.rig.bones_by_id) do
                if b.look_at then
                    -- Compute bone's world-pos by chaining parents.
                    -- For minimal v0.1: assume bone's parent is at puppet origin (torso).
                    -- Simplified: bone world-pos = puppet pos + bone.rest offset.
                    local bone_world_x = p.x + b.rest.x
                    local bone_world_y = p.y + b.rest.y
                    local dx = p.look_target.x - bone_world_x
                    local dy = p.look_target.y - bone_world_y
                    p.bone_state[bid].angle = math.atan(dy, dx)
                end
            end
        end

        -- 3. Advance + apply keyframe animations.
        for anim_id, play_state in pairs(p.playing) do
            local anim = p.animations[anim_id]
            play_state.t = play_state.t + dt * play_state.speed
            if play_state.loop and play_state.t > anim.duration then
                play_state.t = play_state.t % anim.duration
            end
            local frame = M.sample_animation(anim, play_state.t)
            for bid, bone_kf in pairs(frame) do
                -- sample_animation returns degrees; store directly (bone_state
                -- uses degrees for keyframe/procedural channels, radians for
                -- look_at which writes via math.atan).
                p.bone_state[bid].angle = bone_kf.angle
            end
        end

        -- 4. Apply procedural callbacks (via write_bone -- auto-validated).
        -- Use pcall per callback so that a track-conflict from one callback
        -- removes only that offending procedural and re-raises, rather than
        -- leaving other puppets' callbacks un-executed on subsequent calls.
        for name, cb in pairs(p.procedural) do
            local ok, err = pcall(cb, handle, dt)
            if not ok then
                p.procedural[name] = nil  -- disarm offending callback to avoid repeat errors
                error(err, 0)             -- re-raise so caller (or test pcall) sees the conflict
            end
        end
    end
end

-- ====================================================================
-- Rendering (engine.render.* -- only callable in render-phase)
-- ====================================================================
function M.render(handle)
    local p = all_puppets[handle]
    if p == nil then return end

    -- Draw each bone as a rotated rect centered at the bone's world-pos.
    -- v0.1 simplification: bone's world-pos = puppet origin + bone.rest offset.
    -- Bone "length" is approximated by a small constant; later versions will
    -- derive from rig data.
    local BONE_LENGTH = 16
    local BONE_THICKNESS = 4

    for _, b_src in ipairs(p.rig.bones) do
        local b = p.rig.bones_by_id[b_src.id]
        local x = p.x + b.rest.x
        local y = p.y + b.rest.y
        local angle = p.bone_state[b.id].angle
        local c = b.color
        local color = engine.render.rgb(c[1], c[2], c[3])
        engine.render.draw_rect_rotated(x, y, BONE_LENGTH, BONE_THICKNESS, angle, color)
    end
end

-- ====================================================================
-- Asset loading (convenience wrappers around build_rig/build_animation)
-- ====================================================================
-- engine.asset.load_json(path) reads the file and parses JSON in one
-- call, returning a Lua table directly. No separate decode step needed.
function M.load_rig(path)
    local rig_table = engine.asset.load_json(path)
    return M.build_rig(rig_table)
end

function M.load_animation(path, rig)
    local anim_table = engine.asset.load_json(path)
    return M.build_animation(anim_table, rig)
end

return M