// This module defines the Context type, which carries deadlines, cancellation signals,
// and other request-scoped values across API boundaries and between processes.
// Based on:   https://github.com/golang/go/tree/master/src/context
// Last commit: https://github.com/golang/go/commit/52bf14e0e8bdcd73f1ddfb0c4a1d0200097d3ba2
module context

import rand
import time

// A TimerContext carries a timer and a deadline. It embeds a CancelContext to
// implement done and err. It implements cancel by stopping its timer then
// delegating to CancelContext.cancel
pub struct TimerContext {
    id string
mut:
    cancel_ctx CancelContext
    deadline   time.Time
}

// with_deadline returns a copy of the parent context with the deadline adjusted
// to be no later than d. If the parent's deadline is already earlier than d,
// with_deadline(parent, d) is semantically equivalent to parent. The returned
// context's Done channel is closed when the deadline expires, when the returned
// cancel function is called, or when the parent context's Done channel is
// closed, whichever happens first.
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete.
pub fn with_deadline(mut parent Context, d time.Time) (Context, CancelFn) {
    id := rand.uuid_v4()
    if cur := parent.deadline() {
        if cur < d {
            // The current deadline is already sooner than the new one.
            return with_cancel(mut parent)
        }
    }
    cancel_ctx := new_cancel_context(parent)
    mut ctx := &TimerContext{
        cancel_ctx: cancel_ctx
        deadline:   d
        id:         id
    }
    propagate_cancel(mut parent, mut ctx)
    dur := d - time.now()
    if dur.nanoseconds() <= 0 {
        ctx.cancel(true, deadline_exceeded) // deadline has already passed
        cancel_fn := fn [mut ctx] () {
            ctx.cancel(true, canceled)
        }
        return Context(ctx), CancelFn(cancel_fn)
    }

    if ctx.err() is none {
        spawn fn (mut ctx TimerContext, dur time.Duration) {
            time.sleep(dur)
            ctx.cancel(true, deadline_exceeded)
        }(mut ctx, dur)
    }

    cancel_fn := fn [mut ctx] () {
        ctx.cancel(true, canceled)
    }
    return Context(ctx), CancelFn(cancel_fn)
}

// with_timeout returns with_deadline(parent, time.now().add(timeout)).
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete
pub fn with_timeout(mut parent Context, timeout time.Duration) (Context, CancelFn) {
    return with_deadline(mut parent, time.now().add(timeout))
}

// deadline returns the deadline for this context.
pub fn (ctx &TimerContext) deadline() ?time.Time {
    return ctx.deadline
}

// done returns the done channel from the embedded CancelContext.
pub fn (mut ctx TimerContext) done() chan int {
    return ctx.cancel_ctx.done()
}

// err returns the error from the embedded CancelContext.
pub fn (mut ctx TimerContext) err() IError {
    return ctx.cancel_ctx.err()
}

// value returns the value associated with the given key by delegating
// to the embedded CancelContext.
pub fn (ctx &TimerContext) value(key Key) ?Any {
    return ctx.cancel_ctx.value(key)
}

// cancel cancels the timer context by delegating to the embedded CancelContext
// and optionally removing itself from its parent's children.
pub fn (mut ctx TimerContext) cancel(remove_from_parent bool, err IError) {
    ctx.cancel_ctx.cancel(false, err)
    if remove_from_parent {
        // Remove this TimerContext from its parent CancelContext's children.
        mut cc := &ctx.cancel_ctx.context
        remove_child(mut cc, ctx)
    }
}

// str returns a string representation of the TimerContext, showing the
// parent context name, the deadline time, and the duration remaining.
pub fn (ctx &TimerContext) str() string {
    return context_name(ctx.cancel_ctx.context) + '.with_deadline(' + ctx.deadline.str() + ' [' +
        (time.now() - ctx.deadline).str() + '])'
}