module Std::Iter {

import Std::Array::*;

struct Iter<T> {
    data: *T,
    len: uint,
    pos: uint,
}

/* Create an iterator from an Array */
func Array_Iter<T>(arr: *Array<T>) -> Iter<T> {
    return Iter<T> { data: arr.data, len: arr.len, pos: 0 };
}

/* Check if there are more elements */
func Iter_HasNext<T>(it: *Iter<T>) -> bool {
    return it.pos < it.len;
}

/* Get the next element and advance (undefined if HasNext is false) */
func Iter_Next<T>(it: *Iter<T>) -> T {
    let val: T = it.data[it.pos];
    it.pos = it.pos + 1;
    return val;
}

/* Peek current element without advancing (undefined if HasNext is false) */
func Iter_Peek<T>(it: *Iter<T>) -> T {
    return it.data[it.pos];
}

/* Reset iterator to the beginning */
func Iter_Reset<T>(it: *Iter<T>) {
    it.pos = 0;
}

/* Current position */
func Iter_Pos<T>(it: *Iter<T>) -> uint {
    return it.pos;
}

/* Remaining length */
func Iter_Len<T>(it: *Iter<T>) -> uint {
    return it.len;
}

/* Count remaining elements */
func Iter_Count<T>(it: *Iter<T>) -> uint {
    return it.len - it.pos;
}

/* Skip N elements */
func Iter_Skip<T>(it: *Iter<T>, n: uint) {
    it.pos = it.pos + n;
    if it.pos > it.len {
        it.pos = it.len;
    }
}

/* Take first N elements (by limiting len) */
func Iter_Take<T>(it: *Iter<T>, n: uint) -> Iter<T> {
    var endPos: uint = it.pos + n;
    if endPos > it.len {
        endPos = it.len;
    }
    return Iter<T> { data: it.data, len: endPos, pos: it.pos };
}

/* True if any remaining element equals value */
func Iter_AnyEq<T>(it: *Iter<T>, value: T) -> bool {
    var i: uint = it.pos;
    while i < it.len {
        if it.data[i] == value {
            return true;
        }
        i = i + 1;
    }
    return false;
}

/* True if every remaining element equals value (true if empty) */
func Iter_AllEq<T>(it: *Iter<T>, value: T) -> bool {
    var i: uint = it.pos;
    while i < it.len {
        if it.data[i] != value {
            return false;
        }
        i = i + 1;
    }
    return true;
}

/* Collect remaining elements into a new Array */
func Iter_Collect<T>(it: *Iter<T>) -> Array<T> {
    let remaining: uint = it.len - it.pos;
    var cap: uint = remaining;
    if cap == 0 {
        cap = 1;
    }
    var arr: Array<T> = Array_New<T>(cap);
    var i: uint = it.pos;
    while i < it.len {
        Array_Push<T>(&arr, it.data[i]);
        i = i + 1;
    }
    return arr;
}

// ---------------------------------------------------------------------------
// Higher-order helpers (int-specialized; take fat func pointers / closures)
// ---------------------------------------------------------------------------

/* Map each remaining int through f, collect into a new Array */
func Iter_MapInt(it: *Iter<int>, f: func(int) -> int) -> Array<int> {
    let remaining: uint = it.len - it.pos;
    var cap: uint = remaining;
    if cap == 0 {
        cap = 1;
    }
    var out: Array<int> = Array_New<int>(cap);
    var i: uint = it.pos;
    while i < it.len {
        let mapped: int = f(it.data[i]);
        Array_Push<int>(&out, mapped);
        i = i + 1;
    }
    return out;
}

/* Keep remaining ints for which pred returns true */
func Iter_FilterInt(it: *Iter<int>, pred: func(int) -> bool) -> Array<int> {
    let remaining: uint = it.len - it.pos;
    var cap: uint = remaining;
    if cap == 0 {
        cap = 1;
    }
    var out: Array<int> = Array_New<int>(cap);
    var i: uint = it.pos;
    while i < it.len {
        let v: int = it.data[i];
        if pred(v) {
            Array_Push<int>(&out, v);
        }
        i = i + 1;
    }
    return out;
}

/* Left-fold remaining ints: f(f(...f(init, x0), x1), ...) */
func Iter_FoldInt(it: *Iter<int>, init: int, f: func(int, int) -> int) -> int {
    var acc: int = init;
    var i: uint = it.pos;
    while i < it.len {
        acc = f(acc, it.data[i]);
        i = i + 1;
    }
    return acc;
}

/* Call f for each remaining int (side effects; f's return is ignored) */
func Iter_ForEachInt(it: *Iter<int>, f: func(int) -> int) {
    var i: uint = it.pos;
    while i < it.len {
        let _ignored: int = f(it.data[i]);
        i = i + 1;
    }
}

/* True if any remaining element satisfies pred */
func Iter_AnyInt(it: *Iter<int>, pred: func(int) -> bool) -> bool {
    var i: uint = it.pos;
    while i < it.len {
        if pred(it.data[i]) {
            return true;
        }
        i = i + 1;
    }
    return false;
}

/* True if all remaining elements satisfy pred (true if empty) */
func Iter_AllInt(it: *Iter<int>, pred: func(int) -> bool) -> bool {
    var i: uint = it.pos;
    while i < it.len {
        if !pred(it.data[i]) {
            return false;
        }
        i = i + 1;
    }
    return true;
}

/* Sum remaining ints (specialized fold) */
func Iter_SumInt(it: *Iter<int>) -> int {
    var total: int = 0;
    var i: uint = it.pos;
    while i < it.len {
        total = total + it.data[i];
        i = i + 1;
    }
    return total;
}

}