## This needs to be run *before* running the model to avoid the solver
## unlocking problem in deSolve.
requireNamespace("deSolve", quietly = TRUE)

## Workaround for a devtools bug (not sure if new bug or old bug)
if (nzchar(system.file("include", package = "dde"))) {
  Sys.setenv(DDE_INCLUDE = system.file("include", package = "dde"))
} else {
  Sys.setenv(DDE_INCLUDE = "../../inst/include")
}

undesolve <- function(x) {
  x <- unclass(x)
  at <- attributes(x)
  attributes(x) <- at["dim"]
  x
}

## A simple Lorenz attractor
run_lorenz_deSolve <- function(times, tol = 1e-7) {
  sigma <- 10.0
  R     <- 28.0
  b     <-  8.0 / 3.0

  initial <- function(t = 0, pars = NULL) {
    c(10, 1, 1)
  }

  derivs <- function(t, y, .) {
    y1 <- y[[1L]]
    y2 <- y[[2L]]
    y3 <- y[[3L]]
    list(c(sigma * (y2 - y1),
           R * y1 - y2 - y1 * y3,
           -b * y3 + y1 * y2))
  }

  undesolve(deSolve::ode(initial(), times, derivs, atol = tol, rtol = tol))
}

run_seir_deSolve <- function(times, tol = 1e-7) {
  b <- 1 / 10
  N <- 1e7
  beta <- 10
  sigma <- 1 / 3
  delta <- 1 / 21
  lat_hum <- 14
  I0 <- 1

  Births <- N * b
  ## i.e. proportion of humans surviving the latent period
  surv <- exp(-b * lat_hum)

  t0 <- NULL
  y0 <- NULL
  lag <- NULL

  initial <- function(t = 0, pars = NULL) {
    if ("I0" %in% names(pars)) {
      I0 <<- pars$I0
    }
    t0 <<- t
    y0 <<- c(S = N - I0,E = 0, I = I0, R = 0)
    lag <<- make_lagvalue(t0, y0)
    y0
  }

  derivs <- function(t, y, .) {
    S <- y[[1L]]
    E <- y[[2L]]
    I <- y[[3L]]
    R <- y[[4L]]

    ## people developing latent infection
    new_inf <- beta * S * I / N

    ## people that become latent 'lat_hum' days ago, less those that
    ## died during that time
    S_lag <- lag(t, lat_hum, 1L)
    I_lag <- lag(t, lat_hum, 3L)
    lag_inf <- S_lag * I_lag * beta * surv / N

    dS <- Births  - b * S - new_inf + delta * R
    dE <- new_inf - lag_inf - b * E
    dI <- lag_inf - (b + sigma) * I
    dR <- sigma * I - b * R - delta * R

    list(c(dS, dE, dI, dR))
    ## Output variables
    ## c(prev = I/N, Hpop = S+E+I+R))
  }

  make_lagvalue <- function(t0, y0) {
    force(t0)
    y0 <- unname(y0)
    function(t, lag, nr=0L) {
      t1 <- t - lag
      if (t1 > t0) {
        deSolve::lagvalue(t1, nr)
      } else if (length(nr) == 1 && nr == 0L) {
        y0
      } else {
        y0[nr]
      }
    }
  }

  undesolve(deSolve::dede(initial(), times, derivs, atol = tol, rtol = tol))
}

run_lorenz_dde <- function(times, tol = 1e-7, ...) {
  p <- c(10, 28, 8 / 3)
  y <- c(10, 1, 1)
  dopri(y, times, "lorenz", p, atol = tol, rtol = tol, ...,
        dllname = "dde_lorenz")
}

run_seir_dde <- function(times, tol = 1e-7, return_history = FALSE, ...,
                         n_history = 1000L) {
  p <- numeric(0)
  y0 <- c(1e7 - 1, 0, 1, 0)
  dopri(y0, times, "seir", p, atol = tol, rtol = tol, n_history = n_history,
        dllname = "dde_seir", return_history = return_history, ...)
}

.dlls <- local({
  dirs <- c(".", dde_example_path())
  files <- unlist(lapply(dirs, dir, pattern = "\\.c$", full.names = TRUE))
  lapply(files, dde:::shlib, "dde_")
})

drop_attributes <- function(x, keep = c("class", "dim")) {
  at <- attributes(x)
  attributes(x) <- at[names(at) %in% keep]
  x
}

make_null_pointer <- function(p) {
  unserialize(serialize(p, NULL))
}