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import std/[algorithm, math, sugar, strformat]

type
    OscFn* = proc (f: float, t: float): float

    Note* = tuple
        len: float ## seconds
        freq: float
        vol: float
        osc: OscFn

    ProcessedNote* = tuple
        start: float ## absolute time in seconds
        stop: float  ## absolute time in seconds
        freq: float
        vol: float
        osc: OscFn

const HACK_LONGEST_NOTE = 16.0

func process*(music: var seq[ProcessedNote], notes: openArray[Note]; start_init: float, speed: float=1) =
    ## Adds a list of notes to the music list
    ##
    ## `notes`  sequence of notes with no rests in between
    var start = start_init
    var t = start
    for note in notes:
        assert note.len >= 0.0
        assert note.len <= HACK_LONGEST_NOTE, &"note too long: {note.len}"
        start = t
        let stop = t + note.len / speed
        music &= (start, stop, note.freq, note.vol, note.osc)
        t = stop

func sortByStart*(music: var seq[ProcessedNote]) =
    music.sort((a, b) => cmp(a.start, b.start))

func bisect(music: openArray[ProcessedNote], x: float): int =
    ## Return the index where to insert item `x` in list `music`
    ## 
    ## assumes `music` is sorted by `.start`

    music.lowerBound(x, (m, key) => cmp(m.start, key))

const GAIN_BIAS: float = pow(2.0, 31.0)

proc at*(music: openArray[ProcessedNote], t: float): int32 =
    ## Returns the total intensity of music sampled at time t
    ## 
    ## assumes `music` is sorted by `.start`

    var i: int = music.bisect(t) - 1    
    
    var ret: float = 0

    while i >= 0:
        let m = music[i]
        assert m.start <= t
        if m.start + HACK_LONGEST_NOTE < t:
            break
        else:
            ret += m.vol * m.osc(m.freq, t - m.start)
        i -= 1

    ret *= GAIN_BIAS
    
    # clip sample
    clamp(ret, int32.low.float..int32.high.float).int32